How to know whether a number is power of 2

Number	Binary	Number-1	Binary
2	00000010	1	00000001
4	00000100	3	00000011
8	00001000	7	00000111
16	00010000	15	00001111
32	00100000	31	00011111

If n is a power of 2, then n&(n-1) is equal to 0.

public class PowerOfTwo {
 public static boolean isPowerOfTwo(int n) {
  return ((n & (n - 1)) == 0);
 }
}

Following is the junit test case for above program.

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class PowerOfTwoTest {

 @Test
 public void test1() {
  assertTrue(PowerOfTwo.isPowerOfTwo(2));
  assertTrue(PowerOfTwo.isPowerOfTwo(4));
  assertTrue(PowerOfTwo.isPowerOfTwo(8));
  assertTrue(PowerOfTwo.isPowerOfTwo(16));
  assertTrue(PowerOfTwo.isPowerOfTwo(32));
  assertTrue(PowerOfTwo.isPowerOfTwo(64));
  assertTrue(PowerOfTwo.isPowerOfTwo(1));

  assertFalse(PowerOfTwo.isPowerOfTwo(3));
  assertFalse(PowerOfTwo.isPowerOfTwo(5));
  assertFalse(PowerOfTwo.isPowerOfTwo(6));
  assertFalse(PowerOfTwo.isPowerOfTwo(7));
 }
}